A serial scanning type printing apparatus which performs printing by scanning a printhead on a print medium is applied to various image formation. Particularly, in recent years, a printing apparatus based on an ink-jet method is widely used since it is capable of high-resolution color printing to attain an image with greatly-improved image quality.
In the ink-jet printing apparatus, a high-resolution image printing can be realized by increasing the integration density of nozzles to discharge ink droplets while reducing the amount of ink discharge per 1 dot. Further, the reduction of printing speed, as a matter of concern accompanying the improvement in image quality, is excellently prevented by use of multiple printing elements, improvement in driving frequency, or use of, e.g., bidirectional printing of performing printing upon forward scanning and backward scanning of the printhead.
In the printhead including multiple printing elements, a defective printing element (hereinbelow, also referred to as a “defective channel”) occurs in correspondence with frequency of use.
Further, as the number of arrayed printing elements in a high integration density increases, the probability of existence of defective printing element increases upon head manufacturing time. Further, in a case where elements for plural colors are integrally formed for prevention of color shift and improvement of operability, the probability further increases. Even when many printing elements are normal, only 1 defective printing element degrades the image quality.
As countermeasures against the above inconvenience, proposed are various methods for detecting a defective printing element and recovery methods or printing methods in correspondence with the result of detection. Japanese Published Unexamined Patent Application Nos.61-123545, 11-000988, 11-077986, 10-258526 and 2001-063008 disclose countermeasures against a case where the printhead includes a defective printing element.
Japanese Published Unexamined Patent Application No. 61-123545 discloses a method of print-outputting image data corresponding to a defective channel by a normal channel mainly by 1-path printing. When a carriage performs printing in a rightward direction, normal printing is performed, and when the carriage moves in a leftward direction, paper feeding is performed by an integral multiple of 1 pixel, for substitutional printing for a pixel which has not printed by a defective printing element by another normal printing element, then the portion of the defective channel is complemented by the normal channel. According to this method, originally 1-path printing is performed but substantially 2-path printing is performed upon substitutional printing.
Further, Japanese Published Unexamined Patent Application No. 11-077986 discloses, in consideration of the life of a complement nozzle on the complementary printing side, counting the frequency of use of the complement nozzle, and when the total frequency of use becomes a predetermined value, sequentially replacing the complement nozzle with a new nozzle. According to this method, substantially 2-path printing is performed upon substitutional printing as in the case of Japanese Published Unexamined Patent Application No. 61-123545.
Further, Japanese Published Unexamined Patent Application No. 11-000988 discloses setting n/m printing elements, obtained by dividing n elements by a submultiple m of the number of nozzles, as first printing elements, on the other hand, setting n(m−1)/m printing elements as second printing elements not used in normal print scanning, and only when the first printing element is defective, operating the second printing element as a substitutional printing element. This arrangement is premised on multipath printing of completing an image by performing print scanning and paper feed m times basically on the same image area.
Further, Japanese Published Unexamined Patent Application No. 10-258526 discloses completely replacing defect data of one nozzle with data of another nozzle. According to this method, a reference mask is obtained prior to printing, then a defective nozzle is specified, and a substitute nozzle is selected based on the position of the defective nozzle. Thereafter, print data is deleted from the mask of the defective nozzle, and the print data is added to the mask of the substitute nozzle. This method is premised on multipath printing as in the case of Japanese Published Unexamined Patent Application No. 11-000988.
Further, Japanese Publish d Unexamined Patent Application No. 2001-063008 discloses complementing by a printing element parallel to a defective printing element in a print scanning direction. According to this method, a black defective printing element is complemented by cyan, magenta and yellow printing elements.
However, in the countermeasures against a case where the printhead includes a defective printing element as described above, as the number of paths is increased or printing is premised on multipath printing for complementary printing, the throughput is degraded. Further, the method of complementary printing in Japanese Published Unexamined Patent Application No. 2001-063008 premised on 1-path printing, in a case where a dot to be complemented is not conspicuous such as a black dot, there is no problem, however, if a complemented dot is conspicuous such as a cyan, magenta or yellow dot complemented by another color, the technique is not applicable.